Carrying out chemical reactions in which reaction gases are circulated



Sept. 6, 1932. J. HUGHES 1,875,926

CARRYING OUT CHEMICAL REACTIONS IN WHICH REACTION GASES ARE CIRCULATED I Filed March 21, 1928 2 L 1 NH5 OUT qlyhlon ouf Clmuumm PU P I WASHER tM/asmng Lu uid In }M' W MW QWW Patented Sept. 6, 1932 I UNITE ST JOSEPH HUGHES, OF STOCKTON-ON-TEES, ENGLAND, ASSIGNOR TO IMPERIAL GHEMICAL PANY CARRYING our CHEMICAL nnao rions IN WHICH REACTION GASES ABE cIRCULAtrED Application filed March 21,: 1928, Serial No.

In variouschemical operations involving gaseous reagents there are present, or are produced, inertgases which take no part in the desired reactions and which interfere with the economic working of the process, especially in cases where the gases remaining after separation from the desired reaction products are circulated to undergo further reaction. Thus in the synthetic production of ammonia from hydrogenand atmospheric nitrogen, the argon introduced with the nitrogen and the methane introduced with the hydrogen, although present at the start in their valuable constituents has not hitherto been practicable. A similar problem arises in connection with other chemical processes, such as the production of methanol from carbon monoxide and hydrogen. a

The above refers to cases in which the percentage of inert gases is relatively small e. g. 6%. A similar problem arises however when the percentage of inert gases is relatively high e. g. 25 per cent. This case occurs in the Bergius coal hydrogenation process. Here it is usual to reject the gases for hydrogenation purposes after one passage through the a aratus thou h of course the ma be used PP b y y are scrubbed wlth keroseneunderpressure,

for other purposes.

According to the present invention the valuable constituents of the purge gases or in the case of coal hydrogenation of the initial gases are recovered by scrubbing the purge or initial gases under pressure, with a solvent, which dissolves inert gases such as methane and argon in greater proportion than hydrogen and nitrogen or hydrogen alone.

The solvent preferred is paraffin oil, or

kerosene which may be defined as that fraction of oil derived from crude petroleum 283,598, and in Great Britain April 6, 1927,

which is ordinarily used for illuminating" free'the gases absolutely of-inerts, but instead to re1nove,the greatest possiblequantity of inerts per unit time. A high gas rate is-used, since whatever the gas or liquor rate, the liquor always becomes saturated with hydrounit time can be enhanced by increasing the gas rate WlllllOUll lncurring a corresponding increase in loss of hydrogen.- I have further. found that by releasing the pressure on the" washing kerosene, which is charged with gas, in stages, it is possible to secure at the varlous stages gases'containing enhanced proportions of various constituents. Thus by to say 3 atmospheres, the gas evolved from kerosene used to scrub the purge from an ammonia synthesis plant contains the bulk of the absorbed methane, nitrogen and hydrogen.

By further reducing the pressure to atmospheric a gas in which the argon-nitrogen ratio is greater than in the original mixture can be obtained. -My invention therefore includes a process of recovering'valuable gases from gases containing inert constituents, such as argon and methane, wherein the said gases .in which the inert gases are absorbed and from which they are fractionally released by releasing the pressure in stages. The invention. further includes the process of recovering and treating the absorbed gases as hereinafter described. f

An example of an-application of our invention is as follows Purge gas from an ammoniasynthesis plant operating at 200 atmospheres, containing'about 5 per cent of inert gases, 1s scrubbed .65 gen, so that the loss of hydrogen is constant while the amount of inert gas removed per reducing thepressure from 200 atmospheres with kerosene in a tower at the rate of M of oil per 1000-5000 M gas per hour.

The temperature may be the normal, or advantageously somewhat lower e. g. 0 C. No special Cooling of the absorption towers is necessary as the heat of solution appears to be negligible. 2'00 atmospheres pressure,fis restoredto the ammonia synthesis system. The scrubbing oil is collected in a let-down vessel and the pressure a is let down in stages. The gas same by lettingdown to 3 atmospheres contains roughly per cent methane, rather i less nitrogen and about '50 per cent of hydrogen, Power may berecovered from the compressed parafiin by releasing the pressure in a Pelton wheel. The gas produced in ;the second let down to atmospheric pressure is rich in argon, and afterchemical removal of hydrogen and methane (by combustion with oxygen and removal of water and carbon dioxide) contains about 50430 per cent i o argom rest e ng tr e I A -fur ther application of the invention to the. treatment of :gases from the hydrogenationof coal or oil may be cited. Coal is treat ed'with pure hydrogen, or hydrogen containing small quantities of inert gases under the sure, The gaseous resultants comprising hydrogen no Qnteredinto reaction and gases arising jfrom the distillation of the coal, principally methane, are removedfrom the reacti'on vessel and are scrubbed under pressure with kerosene. he scrubbed gas is sent back to the reaction vessel.

Thescrubbing oil employed in the process I of niyinvention is the ordinary parafi'in oil or kerosene of commerce, but closely related i fractions of petroleumdistillates or the like may alsobe ,used.

The accompanying flow sheet illustrates schematically the application of the invention (containing small jam-cunts of argon and to anammonia synthesis plant. I

Compressed nitrogen hydrogen mixture methane) is supplied through compressor 5 to j a circuit 7f.

vice (liquefieror water scrubber) 2. Then the major portion (99%) of the gases passes through the circulating pump S while the rea mainder ispurged'away through pipe 8 and led to washer 4 where it is washed with kerosene to remove inerts, the residual hydrogen I passing through the subsidiary circulation pump Giback to the main circuit.

I declare that what I claim is which includes the steps of causing said gases to react with one another while circulating 7 under pressurepurging away part "of the said gases, scrubbing the purge separately The scrubbed gas, still at about usual conditions of temperature and pres It passes through the catalyst [chamber Iwhere partia'l'conversion into ammonia occurs, and the ammonia removal de- 1. Process of treating gases comprising reactive gases and a small proportion of inerts to react with one another while circulating under pressure purging away part of the said gases, scrubbing separatelyunder pressure with a non volatile solvent which preferentially dissolves the inerts, and returning the purified purge to said process. o, V 4. Process of treating gases comprising reactive gases and a small proportion of inerts which includes the steps of causing said gases to reactwith one another while circulating,

under pressure, purging away part of the said gases, scrubbing separately under pressure with a non volatile solvent which preferentially dissolves the inerts, and returning the purified purge to said process without releasing pressure on same. V

5. Process of treating gases comprising reactive gases anda small proportion of inerts, which includes the steps of causingsaid-gases to react with one another while circulating under pressure, purging away part of the gases, scrubbing separately under pres sure with a non volatilesolvent which preferentially dissolves the inerts, releasing pressure on the solutionin stages, and coll-ecting separately the ases evolved from each stage.

p 6'. Process 0 ammonia synthesis which includes the stepsi of causing gases comprising nitrogen, hydrogen and a small proportion of inerts to interact while circulating under pressure, purgingaway part of the said gases, scrubbing the purge under pressure with paraifin oil, and returning the purge to said process. v V In witness whereof, I have hereunto signed my name this 8th day of March 1928;

- JOSEPH HUGHES.- 

